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Radial Neuropathy

Introduction

  • Nerve roots: C5-T1
  • Sensory:
    • Most of the skin of the posterior side of forearm, the dorsal surface of the lateral side of the palm, and dorsal surface of the lateral three and a half digits.
  • Motor
    • Posterior arm compartment (tricep brachii)
    • Posterior forearm compartment (all extensor muscles in the forearm)

Etiology

  • Middle or distal third humerus fractures (most common)
    • Associated with 12% of all humeral shaft fractures
  • Operative fixation of humeral fractures
  • Callus formation after supracondylar humerus fracture
  • Traction by supinator muscle in radial head dislocations
  • Gunshot wounds
  • Neoplasm
    • Lipomas
  • Compression
    • From falling asleep on one’s own arm (known as “Saturday night palsy”)
    • Crutches
    • Operative room table
    • Pneumatic tourniquet

Anatomy

Anatomic Course

  • The radial nerve has contributions from C5 – T1 nerve roots
  • It is the terminal continuation of the posterior cord, which travels dorsally to the axillary artery and vein
  • The radial nerve exits the inferior axilla via the triangular interval 
    • Here, it supplies branches to the long and lateral heads of the triceps brachii
  • It then takes a spiral course around the humerus
    • It continues distal down the posterior arm in a shallow depression in the humerus called the radial groove
  • It then wraps around the humerus laterally to give off a branch to the medial head of the triceps brachii
  • It travels anterior to the lateral epicondyle of the humerus to enter the forearm 
  • It then divides into two terminal branches:
    • Deep branch (motor)
      • Once the deep branch penetrates the supinator muscle, it becomes known as the posterior interosseous nerve (PIN)
    • Superficial branch (sensory)
  • The radial nerve has an anatomical course proximal below the lateral intermuscular septum and continues distal between the brachialis and brachioradialis muscles. The entrapment point involves the tendinous lateral intermuscular septum and provocative tests will be positive at this. This is a location that is prone to radial nerve injury during humeral factures. Release of the radial nerve at this level involves dividing the lateral intermuscular septum, while protecting the posterior brachial and antebrachial cutaneous nerves that have an adjacent course to the radial nerve proper. The surgical approach involves dissecting the interval between the brachialis and brachioradialis to identify the radial nerve. In this case, the patient presented with pain originating from the neck that radiated along the course of the posterior division and radial nerve. Her C-spine surgery failed and was referred to our institution. Positive provocative tests included the neck, spiral groove, arcade of Frohse, and radial sensory nerve entrapment. The hierarchical scratch collapse test was used. Radial nerve releases were elected at three sites of entrapment in the upper extremity. This video details the release at the spiral groove.

Anatomic Points of Compression

In the arm:

  • Lateral intermuscular septum
    • Formed by the lateral head of the triceps

In the forearm: